Display screen or portion thereof with transitional graphical user interface



FIG. 1 is a first image in a sequence of a display screen or portionthereof with transitional graphical user interface showing my newdesign; and,

FIG. 2 is a second image thereof.

The outermost broken lines showing the display screen or portion thereofare for environmental purposes only and form no part of the claimeddesign.

The remaining broken lines in the figures show portions of thetransitional graphical user interface which form no part of the claimeddesign.

The appearance of the transitional graphical user interface sequentiallytransitions between the images shown in FIGS. 1 and 2. The process orperiod in which one image transitions to another forms no part of theclaimed design.

CLAIM I claim the ornamental design for a display screen or portionthereof with transitional graphical user interface, as shown anddescribed.